The Varied Types of Gasifiers – Advantages and Disadvantages

Gasification is a process that converts the fossil fuel or organic waste into gases. These gases include Hydrogen (H2), Carbon Dioxide (CO2) and Carbon Monoxide (CO). The process involves oxidation and reduction of the organic matter at high temperatures. The product is a gas mixture/fuel called producer gas or synthesis gas. This product is combustible at higher temperatures, hence is more efficient than the combustion of the original fuels. This process is extensively used to generate the electricity in varied industries.

Types of Gasifier

On the basis of the flow of oxygen in the gasifier equipment, categorization of gasifier can be done into further types. The primary classification involves – Updraught, Downdraught and Cross-draught.

The choice and type of the gasifier depends on the

• Type of fuel
• Size of fuel
• Solid Wastes
• Form
• Moisture and ash content
• The flow of oxygen in the Gasifier

Updraught Gasifier

Also called the countercurrent gasifier, this is the simplest and the oldest one. In the upper part of the gasifier, the pyrolysis occurs due to the heat transfer. While in the lower part, combustion takes place followed by reduction. This takes place at a potentially higher temperature. During the process, the tars and volatiles are carried in the gas stream. The ashes and other residues are also removed from the bottom of this reactor.

Advantages:

• The major advantage is its simplicity.
• The internal heat exchange and high charcoal release gases at low temperatures.
• High gasifier equipment efficiency.

Drawbacks:

• Explosive situations may arise if there is channelling in the equipment. This is can be the cause for oxygen breakthrough. This is extremely dangerous and is one of the major drawbacks of this gasifier.
• Tars can be burnt if the gas is used for applications with some direct heat exposure.
• The disposal of condensates that contain tar can also be a minor problem.  

Downdraught Gasifier

This serves as a solution to the problem of tar in the gas stream. This designed gasifier is also called the co-current one. Here, the air/oxygen is introduced above the oxidation zone. The produced producer gas or synthetic gas is removed from the bottom thus, making the gas and fuel move in the same direction. Due to the fuel and gases in motion, the distilled products and acid are converted into gases like Methane, Carbon Monoxide, Hydrogen and Carbon Dioxide.

Advantages:

• The product obtained is the tar-free gas that can be used for engine applications.
• Due to the presence of a lower level of organic components in the condensate, these gasifiers suffer less from any environment sort of objections.

Drawbacks:

• Unable to operate on the majority of unprocessed fuels.
• They suffer from problems due to fuels with high ash content.
• There is a lack of internal heat exchange in comparison to the updraught gasifier.
• Less efficiency due to the low heating value of gases.
• The gasifier can turn inefficient under high uniform temperatures and may become impractical for power ranges above 350 kW.

Cross-draught gasifier

Cross-draught gasifiers are used for the gasification of charcoal. This takes place at extremely high temperatures in the zone where oxidation occurs.

Advantages:

• The installations can be economically feasible below power range of 10kW.
• It can be operated on a very small scale.
• These type of gasifiers can be a fit for the small engines.

Disadvantages:

• It needs a consequent supply of high-quality charcoal.
• These gasifiers have minimal tar-converting capabilities.

Categorization of Gasifiers based on solid wastes

Empty Fruit Bunch Gasifier

This is a novel gasifier, developed without briquetting for the use of the Empty Fruit Bunch. This gasifier needs to be pressed to lower the moisture content and the ash content. The moisture content should be brought down to around 20% while the ash content to 5%. Also, the ash needs to be softened at temperatures greater than 1,200°C before providing it to the gasifier.

However, some dimensions need to be taken care of. The size of the EFB should not exceed beyond 200 X 200 X 90 mm. Also, the bulk density should be above 150 kg/m³.

These reactors with such varied efficiencies and power ranges can serve different purposes for waste management. Also, the different by-products can further be used for various applications.